User Contributed Notes 14 notes

[Editor's note: put your includes in the beginning of your script. You can call an included function, after it has been included --jeroen]

The documentation states: "In PHP 3, functions must be defined before they are referenced. No such requirement exists in PHP 4."

I thought it wise to note here that there is in fact a limitation: you cannot bury your function in an include() or require(). If the function is in an include()'d file, there is NO way to call that function beforehand. The workaround is to put the function directly in the file that calls the function.

According to the specified regular expression ([a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*), a function name like this one is valid:

<?php
function €()
{
echo 'foo';
}
?>

And PHP interpreter correctly interprets the function. However some parsers (ex: PDT/Eclipse) does not see this as a valid function name, and only accept function names starting with a letter or an underscore.

Stack overflow means your function called itself recursivly too many times and just completely filled up the processes stack. That error is there to stop a recursive call from completely taking up the entire system memory.

If you want to validate that a string could be a valid function name, watch out. preg_match() matches anywhere inside the test string, so strings like 'foo#' and ' bar' will pass with the regex that they give ([a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*)

The solution is to use anchors in the regex (^ and $) and check the offset of the match (using PREG_OFFSET_CAPTURE).

function function_name($arg_1, $arg_2, ..., $arg_n){ code_line1; code_line2; code_line3; return ($value); //stops execution of the function and returns its argument as the value at the point where the function was called.}One may have more than one return()statements in a function.*/

$text= 'This Line is Bold and Italics.'; function makebold_n_italics($text) {$text = "<i><b>$text</i></b>"; return($text); //the return() statement immediately ends execution of the current function, and returns its argument as the value of the function call in print command} print("This Line is not Bold.<br>\n"); print("This Line is not Italics.<br>\n"); echo makebold_n_italics("$text") ,"--->", 'It prints the returned value of variable $text when function is called.'."<br>\n"; echo "$text", '---> prints the original value of variable $text.'."<br>\n"; // prints the original value of $text$thanks='Thanks to Zeev Suraski and Andi Gutmans !!!';$text=$thanks; echo makebold_n_italics("$text");

/*Above codes produces output in a browser as under:

This Line is not Bold.This Line is not Italics.This Line is Bold and Italics.--->It prints the returned value of variable $text when function is called.This Line is Bold and Italics.---> prints the original value of variable $text.Thanks to Zeev Suraski and Andi Gutmans !!!*/?>

As a corollary to other people's contributions in this section, you have to be careful when transforming a piece of code in to a function (say F1). If this piece of code contains calls to another function (say F2), then each variable used in F2 and defined in F1 must be declared as GLOBAL both in F1 and F2. This is tricky.

Take care when using parameters passed by reference to return new values in it:

<?PHP

function foo( &$refArray, ....) {

UNSET($refArray); //<-- fatal!!!

for (....) {$refArray[] = .... }//end for

}//end foo

?>

I tried to make sure the passed variable is empty so i can fill it up as an array. So i put the UNSET. Unfortunately, this seems to cause a loss with the reference to the passed variable: the filled array was NOT returned in the passed argument refArray!

If you're frustrated by not having access to global variables from within your functions, instead of declaring each one (particularly if you don't know them all) there are a couple of workarounds...

If your function just needs to read global variables...

function aCoolFunction () { extract($GLOBALS);....

This creates a copy of all the global variables in the function scope. Notice that because it's a copy of the variables, changing them won't affect the variables outside the function and the copies are lost at the conclusion of the function.

If you need to write to your global variables, I haven't tested it, but you could probably loop through the $GLOBALS array and make a "global" declaration for each one. Then you could modify the variables.

Please note that this shouldn't be standard practice, but only in the case where a function needs access to all the global variables when they may be different from one call to another. Use the "global var1, var2..." declaration where possible.

Important Note to All New Users: functions do NOT have default access to GLOBAL variables. You must specify globals as such in your function using the 'global' type/keyword. See the section on variables:scope.

This note should also be added to the documentation, as it would help the majority of programmers who use languages where globals are, well, global (that is, available from anywhere). The scoping rules should also not be buried in subsection 4 of the variables section. It should be front and center because I think this is probably one of the most non-standard and thus confusing design choices of PHP.

[Ed. note: the variables $_GET, $_POST, $_REQUEST, $_SESSION, and $_FILES are superglobals, which means you don't need the global keyword to use them inside a function]